Fish food web bioaccumualtion model:

Goal:

To evaluate the model performance characterizing and predicting values in three samples systems (Joint Base Andrews, JBA, in spring and summer, and Willow Grove). In a given system, each species is described by the mean body size of all collected fish, and the system is described by the mean measured temperature, dissolved oxygen levels, organic carbon when available. No invertebrates were found or sampled in these systems.

The model:

The food web model is adapted from Sun et al 2020.

Metrics of model performance:

  1. \(R^2\) (full model, by PFAA, by Species)

\(R^2 = 1-RSS / TSS\)

where RSS = residual sum squared and TSS = total sum squared

  1. Model bias (MB) as described in Arnot and Gobas 2004.

\(MB_i = 10^{\frac{\sum_{i=1}^{n} log (C_{model, i} / C_{obs, i})}{n}}\) \(MB_j= 10^{\frac{\sum_{j=1}^{m} log (C_{model, j} / C_{obs, j})}{m}}\)

n = number of chemicals in a given species m = number of species for a given chemical C[model] = predicted PFAA concentration C[obs] = observed PFAA concentration i = number of species j = number of chemicals

In all cases the food web relies on assumptions of relative species feeding interactions


1. Willow Grove

The model predictions for Willow Grove. This system has 3 fish species, and was samples in fall.

Figure 1.

PFAS predictions in Willow Grove system. (A) The PFAS in each diet item were known and provided during the modelling. (B) The PFAS values were estimated based on the food web trophic interactions, the only known PFAS values here were in water and sediment. The dot models values when fish tissue PFAS, water, and sediment values are at their measured mean values. The food web structure was the same between both cases. The dotted lines mark log values of 2 and 10 showing where values are over- or under-predicted by a factor or 2 and 10 respectively.



2. Joint Base Andrews (spring)

The model predictions for JBA in spring season. This system has 8 fish species, and was samples in spring.

Figure 2.

PFAS predictions in JBA system in spring season. (A) The PFAS in each diet item were known and provided during the modelling. (B) The PFAS values were estimated based on the food web trophic interactions, the only known PFAS values here were in water and sediment. The dot models values when fish tissue PFAS, water, and sediment values are at their measured mean values. The food web structure was the same between both cases. The dotted lines mark log values of 2 and 10 showing where values are over- or under-predicted by a factor or 2 and 10 respectively.



3. Joint Base Andrews (summer)

Figure 3.

PFAS predictions in JBA system in summer season. (A) The PFAS in each diet item were known and provided during the modelling. (B) The PFAS values were estimated based on the food web trophic interactions, the only known PFAS values here were in water and sediment. The dot models values when fish tissue PFAS, water, and sediment values are at their measured mean values. The food web structure was the same between both cases. The dotted lines mark log values of 2 and 10 showing where values are over- or under-predicted by a factor or 2 and 10 respectively.



Main figures, all systems together

Figure 4.

PFAS predictions in all systems together. (A) The PFAS in each diet item were known and provided during the modelling. (B) The PFAS values were estimated based on the food web trophic interactions, the only known PFAS values here were in water and sediment. The dot models values when fish tissue PFAS, water, and sediment values are at their measured mean values. The food web structure was the same between both cases. The dotted lines mark log values of 2 and 10 showing where values are over- or under-predicted by a factor or 2 and 10 respectively.



Figure 5.

Model bias in each system by PFAS. The perfect fit is at MB = 1. When values reach 2 and 0.5, they are systematically over-predicted or under-predicted by a factor of two, respectively.

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Figure 6.

Model bias in each system by species. The perfect fit is at MB = 1. When values reach 2 and 0.5, they are systematically over-predicted or under-predicted by a factor of two, respectively.

Contributions to PFAA bioaccumulation via diet and water

Figure 7.

The predicted % contribution from gill uptake and dietary uptake in total PFAS uptake in each fish species in each system. JBA = Joint Base Andrews. WG = Willow Grove. Species Abbreviations:


Figure 8.

The modeled uptake rates and elimination of PFAS by each species.


Figure 9.

The % uptake that come from diet is positively correlated with total PFAS tissue bioaccumulation. Each dot is a species.


Figure 10.

Dietary PFAS uptake (%) is higher in fish at higher trophic levels.


Figure 11

The chain length of perfluoroalkyl carboxylic acids (PFCA) and perfluorosulfonic acids (PFSA) and the % diet contribution in total PFAS uptake. Each dot is species; all systems are presented together.


Figure 12

The chain length of perfluoroalkyl carboxylic acids (PFCA) and perfluorosulfonic acids (PFSA) and their tissue bioaccumulation. Each dot is species; all systems are presented together. The open circles are observed values, the closed circles are modeled values.


Figure 13

Predicted positive relationship between sediment:water PFAS ratio and fish tissue bioconcentrations. The higher ratios are when water is dominant in source of system PFAS. The total PFAS bioaccumulation in fish increases when. Each dot is a species. The size is proportional to sediment PFAS concentrations (ng/g).


Figure 14

Predicted positive relationship between sediment:water PFAS ratio and fish tissue bioconcentrations. The higher the ratio the more sediment (ng/g) PFAS in relation to water PFAS (ml/L) the higher total PFAS bioaccumulation in fish. Each dot is a species.

Sediment:Water ratio data: visualize

Figure 15

Predicted positive relationship between sediment:water PFAS ratio and fish tissue bioconcentrations. The higher ratios are when sediment is dominant in source of system PFAS. Each dot/line is a species.


Figure 16

Relationship between sediment:water PFAS ratio and % diet uptake. The higher ratios are when sediment is dominant in source of system PFAS. Lines connect species.